ValueError: invalid literal for int() with base 10: 'F'

[sentry-io]

Sentry Issue: MICROMASTERS-5FW

ValueError: invalid literal for int() with base 10: 'F'
(14 additional frame(s) were not displayed)
...
  File "django/db/models/sql/query.py", line 1251, in build_filter
    condition = self.build_lookup(lookups, col, value)
  File "django/db/models/sql/query.py", line 1116, in build_lookup
    lookup = lookup_class(lhs, rhs)
  File "django/db/models/lookups.py", line 20, in __init__
    self.rhs = self.get_prep_lookup()
  File "django/db/models/lookups.py", line 70, in get_prep_lookup
    return self.lhs.output_field.get_prep_value(self.rhs)
  File "django/db/models/fields/__init__.py", line 972, in get_prep_value
    return int(value)